Just noticed my home page which has always displayed ads that were right on topic is showing ads for hotels in hondorus and others that are totally unrelated to my site. I have great google positions for keywords related to my site and the field is very popular with advertisers so I assume it's a bug of some sort.
It's not a bug as such, but the bot can zoom in on the wrong keywords. Are there any keywords in the text that might be triggering the wrong ads? You can always try section targeting to get the bot to ignore words and phrases.
Do you already have section targeting? If so, you might be focusing on text that it's picking up on inadvertantly? In my brief experimentation with this, I found that having no section targeting at all worked best for me.
You might find that re-writing the page helps targeting, and avoiding or rephrasing words or phrases that might be triggering the wrong ads. Maybe the count of certain keywords is too high / too low?
I have had an instance where there were no changes to the page, but the bot decided to show totally irrelevant ads. I did email Google on that ocasion and it was resolved, but as a rule irrelevant ads are going to be due to page content, and it's necessary to modify the page accordingly.
My site about Elbonian Widgets tends to get ads concentrating on other Elbonian topics rather than the primary subject of widgets. As visitors are primarily local and repeats I don't worry too much about it.
My adds are irrelevant because my site is about the long price trend of widgets in both Australian and US dollars. I'm getting ads for currency conversion when it would be much more appropriate to have ads about widgets. Google knows my site is about widgets because it sends me search traffic looking for information about it. I wonder when Adsense will catch up with the main search algo.